1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly to an organic light emitting display device capable of displaying two images with one display unit.
2. Description of Related Art
In recent years, a variety of flat panel display devices have been developed with reduced weight and volume in comparison to a cathode ray tube (CRT) display. Some examples of the flat panel display devices include liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display, etc.
Among the various flat panel display devices, the organic light emitting display displays an image by using organic light emitting diodes (OLEDs) to emit light through the recombination of electrons and holes. The organic light emitting display has a rapid response time and low power consumption.
FIG. 1 is a schematic circuit diagram showing a pixel circuit of a conventional organic light emitting display device.
Referring to FIG. 1, a pixel 4 of the conventional organic light emitting display device includes an OLED and a pixel circuit 2 coupled to a data line (Dm) and a scan line (Sn) to control the OLED.
An anode electrode of the OLED is coupled to the pixel circuit 2, and a cathode electrode is coupled to a second power source (ELVSS). The OLED generates light with a luminance (e.g., a predetermined luminance) according to an electrical current supplied from the pixel circuit 2. The pixel circuit 2 controls the magnitude of the electrical current, which is supplied to the OLED, to correspond to a data signal supplied to the data line (Dm) when a scan signal is supplied to the scan line (Sn).
The pixel circuit 2 includes a second transistor (M2) coupled between a first power source (ELVDD) and the OLED, a first transistor (M1) coupled between the second transistor (M2) and the data line (Dm) and the scan line (Sn), and a storage capacitor (Cst) coupled between a gate electrode and a first electrode of the second transistor (M2).
A gate electrode of the first transistor (M1) is coupled to the scan line (Sn), a first electrode of the first transistor (M1) is coupled to the data line (Dm), and a second electrode of the first transistor (M1) is coupled to a terminal of the storage capacitor (Cst).
The first electrode of the first transistor (M1) or the second transistor (M2) can be a source electrode or a drain electrode, and the second electrode is different from the first electrode. For example, when the first electrode is a source electrode, the second electrode is a drain electrode, and vice versa. The first transistor (M1) coupled to the scan line (Sn) and the data line (Dm) is turned on when a scan signal is supplied to the scan line (Sn) to supply a data signal, which is supplied from the data line (Dm), to the storage capacitor (Cst). Thus, the storage capacitor (Cst) is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor (M2) is coupled to one terminal of the storage capacitor (Cst), and the first electrode of the second transistor (M2) is coupled to the other terminal of the storage capacitor (Cst) and the first power source (ELVDD). Further, a second electrode of the second transistor (M2) is coupled to the anode electrode of the OLED.
The second transistor (M2) controls the magnitude of an electrical current to correspond to a voltage value stored in the storage capacitor (Cst), and the electrical current flows from the first power source (ELVDD) to the second power source (ELVSS) via the OLED. The OLED generates light corresponding to the magnitude of the electrical current supplied from the second transistor (M2).
However, the pixel 4 in a conventional organic light emitting display device is coupled to only one OLED. Therefore, the conventional organic light emitting display device has a display unit that includes a plurality of the pixels 4 can only display one image expressed on one surface thereof.